This invention relates to a process for the removal of hydrogen sulfide from gaseous mixtures by simultaneous absorption and oxidation of H.sub.2 S with an aqueous, alkaline scrubbing agent containing pentavalent vanadium as the oxidizing agent, and wherein the reduced scrubbing agent is regenerated in the presence of a promoter by reoxidation of the tetravalent vanadium, and reused. The invention is particularly directed to novel promoters.
It is known from British Pat. No. 1,488,659 for the H.sub.2 S-containing gas to be purified to be scrubbed with an aqueous, alkaline solution, such as a sodium carbonate solution having a pH of between 8 and 9 and containing a soluble salt, such as the sodium salt of anthraquinone disulfonic acid and a metallic vanadate, the vanadium being present in the pentavalent oxidation stage. The absorbed hydrogen sulfide is ionized in the solution with the formation of HS.sup.- ions which reduce the vanadium into the tetravalent oxidation stage, thus liberating elemental sulfur. The thus-reduced vanadium can be reoxidized by an oxidation reaction with an oxygen-containing gas in the presence of a promoter, such as, for example, anthraquinone disulfonic acid (ADS). To maintain the vanadium in solution in the presence of hydrogen sulfide, a complexing agent in the form of tartaric acid, for example, can also be added to the scrubbing solution. This process based on ADS, while satisfactory in many respects, is relatively costly, and on occasion is beset with technical difficulties. Another process is known from U.S. Pat. No. 4,283,379. A still further process is that described in U.S. Pat. No. 4,036,942, wherein the oxidation-reduction of the metal chelate reaction system is conducted concurrently and wherein, according to claim 1 of the patent, the gaseous stream is always contacted with free oxygen and an aqueous solution of the catalyst.